A conventional intercom apparatus with a camera includes an intercom slave that maybe simply referred to as a “slave” hereinafter and is formed of a call switch used by a visitor for calling a resident, a set of a microphone and a speaker used for speech communications between the visitor and the resident, and a camera for taking an image of the visitor. The intercom system also includes an intercom master which will be simply referred to as a “master” hereinafter, is connected to the slave through a non-polar analog two-wire line and is formed of a display displaying an image taken by a slave imaging unit as well as a microphone and a speaker for speech communications with the visitor. The intercom system further includes a sub-master that can make communications with the visitor similarly to the master, and has substantially the same structure as the master.
Each of the master and the sub-master includes a data compression/expansion unit for compressing or expanding video and audio data provided from the slave, a data communication unit performing simultaneous data transmission and reception between the master and the sub-master, and a control unit controlling data processing, communications and the like. The master and the sub-master are connected together over a Local Area Network (LAN) through communication units that arranged in the master and the sub-master, respectively.
Since the master and the sub-master are connected together through a LAN cable, these can transmit data of sounds, characteristics, images and the like to and from a communication terminal inside an external network when a LAN home gateway connecting the indoor LAN cable to the external network is arranged in or around a house. Likewise, these may be connected to an ISDN (Integrated Service Digital Network) line through a router, a DSU (Digital Service Unit) and the like, and thereby the Internet becomes available (Japanese Patent Laying-Open No. 2003-078629 (Patent Document 1)). The ISDN is a digitized public communications network, and is the integrated services digital network over which a user can use services such as telephone, facsimile, data communications and the like through a single interface.
Another video intercom system is also proposed. This system includes a control unit that connects a camera-equipped intercom slave to a home network connecting a plurality of home electric devices and house facilities together for transmitting and receiving data, and connects the camera-equipped intercom slave to general-purpose devices such as a television receiver, a telephone and the like over the network. There is still another video intercom system (Japanese Patent Laying-Open No. 2004-289657 (Patent Document 2)). In this system, a general-purpose device that cannot be directly connected to the home network is connected to it through a conversion interface block.
There has been a system in which a portable audio terminal for performing speech communications is independent of a video terminal for transmitting and receiving images, and call setting is processed on an management server side so that the portable audio terminal can be combined with the video terminal during speech communications by the portable audio terminal, and can be used as a video telephone. This structure of the video telephone system includes the video terminal for transmitting and receiving images, the audio terminal for transmitting and receiving sounds by radio, wireless-to-wired communications converter terminal for mutual conversion between wireless and wired communications, managing means for managing terminal information about a plurality of video terminals and audio terminals, call control means for controlling calling between the terminals according to the information in the managing means, and a management server formed of communication control means performing communications with the audio and video terminals. In this structure, the management server performs the control until a logical audio data channel opens between the audio terminals and a logical data channel opens between the video terminals (Japanese Patent Laying-Open No. 2004-165949 (Patent Document 3)).    Patent Document 1: Japanese Patent Laying-Open No. 2003-078629    Patent Document 2: Japanese Patent Laying-Open No. 2004-289657    Patent Document 3: Japanese Patent Laying-Open No. 2004-165949